Contribution of new photosynthetic assimilates to respiration by perennial grasses and shrubs: residence times and allocation patterns


Author for correspondence: Mariah S. Carbone Tel: +1 949 8241987 Fax: +1 949 8243874 Email:


  • • Quantification of the fate of carbon (C) used by plant metabolism is necessary to improve predictions of terrestrial ecosystem respiration and its sources.
  • • Here, a dual isotope (13C and 14C) pulse-label was used to determine the allocation of new C to different respiratory pathways in the early and late growing seasons for two plant functional types, perennial grasses and shrubs, in the Owens Valley, CA, USA.
  • • Allocation differences between plant types exceeded seasonal allocation variation. Grasses respired 71 and 64% and shrubs respired 22 and 17% of the label below-ground in the early and late growing seasons, respectively. Across seasons and plant types, ~48–61% of the label recovered was respired in 24 h, ~68–84% in 6 d, and ~16–33% in 6–36 d after labeling.
  • • Three C pools were identified for plant metabolism: a fast pool with mean residence times (MRTs) of ~0.5 and ~1 d below- and above-ground, respectively; an intermediate pool with MRTs of 19.9 and 18.9 d; and a storage pool detected in new leaf early growing season respiration > 9 months after assimilation. Differences in allocation to fast vs intermediate C pools resulted in the mean age of C respired by shrubs being shorter (3.8–4.5 d) than that of the grasses (4.8–8.2 d).